DC-DC switching power converters are often used when a system needing a regulated power supply is powered from an unregulated DC source of power, or a regulated DC source of power at a different voltage. Typically, switching power converters are used when either the output voltage is higher than the input voltage, or the input voltage is higher than the output voltage, but not both. However, some applications require a switching power converter that can supply an output voltage that may be either higher or lower than an input voltage. One example is a battery powered system needing a regulated supply voltage at 3 volts DC. The battery supplying the battery powered system may be a lithium battery having an output voltage that varies from 3.3 volts DC down to 2.5 volts DC. A switching power converter that has an output voltage higher than the input voltage may be referred to as a boost converter. A switching power converter that has an output voltage lower than the input voltage may be referred to as a buck converter. By cascading a buck converter and a boost converter, a switching power converter can be created that can supply an output voltage that may be either higher or lower than an input voltage.
A switching power converter typically operates with a switching frequency. During each cycle of the switching frequency, an energy storage element, such as an inductor, is switched to receive power from an input power source for one portion of the cycle. For another portion of the cycle, the energy storage element is switched to provide some of its stored energy to downstream circuitry. The percentage of the cycle that the energy storage element is switched to receive power is known as the duty-cycle, which is varied to regulate the output of the switching power converter.
A switching power converter may be arranged with a DC power source feeding a boost power converter, which feeds a buck power converter that provides the DC output. Typically, such switching power converters employ more than one inductor for energy storage. As a result, switching power converters having both a boost converter and buck converter are larger and not as energy efficient as desired. What is needed is a switching power converter that employs only a single inductor in a buck converter stage that provides a simpler, smaller, and more energy efficient solution.